Surface modification method and surface modification device

Abstract

Provided is a surface modification method for using plasma of a treatment gas to modify a bonding surface of a substrate to be bonded to another substrate, the surface modification method comprising a first adjustment step, an evacuation step, a second adjustment step, and a modification step. In the first adjustment step, the moisture content in a treatment container that can accommodate the substrate is adjusted by supplying a humidified gas at a first flow rate into the treatment container. In the evacuation step, the inside of the treatment container is evacuated after the first adjustment step. In the second adjustment step, the moisture content in the treatment container is adjusted by supplying the humidified gas into the treatment container at a second flow rate greater than the first flow rate. In the modification step, after the second adjustment step, the bonding surface of the substrate is modified by generating a plasma of the treatment gas in the treatment container.

Description

Surface Modification Method and Surface Modification Apparatus

[0001] The present disclosure relates to a surface modification method and a surface modification apparatus.

[0002] Conventionally, as a method of bonding substrates such as semiconductor wafers, a method is known in which the surface to be bonded of the substrate is modified, the surface of the modified substrate is hydrophilized, and the hydrophilized substrates are bonded by van der Waals forces and hydrogen bonds (intermolecular forces).

[0003] The surface modification of the substrate is performed using a surface modification apparatus. The surface modification apparatus accommodates the substrate in a processing container and modifies the surface of the accommodated substrate by the plasma of the processing gas.

[0004] International Publication No. 2018 / 084285

[0005] The present disclosure provides a technique capable of suppressing a decrease in the bonding strength between the substrates to be bonded.

[0006] A surface modification method according to an aspect of the present disclosure is a surface modification method in which a bonding surface of a substrate to be bonded to another substrate is modified by the plasma of a processing gas, and includes a first adjustment step, a evacuation step, a second adjustment step, and a modification step. The first adjustment step adjusts the amount of moisture in the processing container by supplying a humidified gas into the processing container capable of accommodating the substrate at a first flow rate. The evacuation step evacuates the inside of the processing container after the first adjustment step. The second adjustment step adjusts the amount of moisture in the processing container by supplying a humidified gas into the processing container at a second flow rate greater than the first flow rate. The modification step modifies the bonding surface of the substrate by generating the plasma of the processing gas in the processing container after the second adjustment step.

[0007] According to the present disclosure, there is an effect that a decrease in the bonding strength between the substrates to be bonded can be suppressed.

[0008] Figure 1 is a schematic plan view showing the configuration of the bonding system according to the embodiment. Figure 2 is a schematic side view showing the configuration of the bonding system according to the embodiment. Figure 3 is a schematic side view of the upper wafer and lower wafer according to the embodiment. Figure 4 is a schematic cross-sectional view showing the configuration of the surface modification apparatus according to the embodiment. Figure 5 is a magnified view showing the vicinity of the inner wall surface of the processing container according to the embodiment. Figure 6 is a schematic plan view showing the configuration of the bonding apparatus according to the embodiment. Figure 7 is a schematic side view showing the configuration of the bonding apparatus according to the embodiment. Figure 8 is a schematic diagram showing the upper chuck and lower chuck according to the embodiment. Figure 9 is a flowchart showing the processing procedure executed by the bonding system according to the embodiment. Figure 10 is a timing chart showing the operation of each part when modifying the bonding surface of the upper wafer and lower wafer in the bonding process according to the embodiment. Figure 11 is a diagram illustrating an example of the measurement results of the moisture content in the processing container. Figure 12 is a diagram illustrating an example of the measurement results of the moisture content in the processing container.

[0009] The embodiments of the surface modification method and surface modification apparatus disclosed herein will be described in detail below with reference to the drawings. However, the disclosed technology is not limited to the embodiments described below. Furthermore, it should be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. In addition, there may be differences in dimensional relationships and ratios between different parts of the drawings.

[0010] Incidentally, when surface modification of a substrate is repeatedly performed in the processing container of a surface modification apparatus, the amount of moisture in the processing container gradually decreases due to vacuuming, etc. When the amount of moisture in the processing container decreases, the state of the plasma of the processing gas generated in the processing container changes, and the surface modification of the substrate is not performed sufficiently. As a result, the bonding strength between substrates obtained when a modified substrate is joined to another substrate may decrease. A decrease in bonding strength is undesirable as it can cause defects such as substrate delamination. Therefore, there is a need for a technology that can suppress the decrease in bonding strength between substrates being joined.

[0011] <Configuration of the Bonding System> First, the configuration of the bonding system 1 according to the embodiment will be described with reference to Figures 1 to 3. Figure 1 is a schematic plan view showing the configuration of the bonding system 1 according to the embodiment, and Figure 2 is a schematic side view thereof. Figure 3 is a schematic side view of the upper wafer W1 and lower wafer W2 according to the embodiment. Note that in the drawings referred to below, a Cartesian coordinate system in which the vertically upward direction is the positive direction of the Z axis may be shown in order to make the explanation easier to understand.

[0012] The bonding system 1 shown in Figure 1 forms a polymerized wafer T by bonding a first substrate W1 and a second substrate W2.

[0013] The first substrate W1 is a semiconductor substrate, such as a silicon wafer or a compound semiconductor wafer, on which multiple electronic circuits are formed. The second substrate W2 is a bare wafer on which no electronic circuits are formed. The first substrate W1 and the second substrate W2 have approximately the same diameter. Electronic circuits may be formed on the second substrate W2.

[0014] In the following, the first substrate W1 will be referred to as "upper wafer W1," and the second substrate W2 will be referred to as "lower wafer W2." That is, upper wafer W1 is an example of the first substrate, and lower wafer W2 is an example of the second substrate. Also, when referring to upper wafer W1 and lower wafer W2 collectively, they may be referred to as "wafer W."

[0015] Furthermore, as shown in Figure 3 below, the surface of the upper wafer W1 that is joined to the lower wafer W2 will be referred to as the "joining surface W1j," and the surface opposite to the joining surface W1j will be referred to as the "non-joining surface W1n." Similarly, the surface of the lower wafer W2 that is joined to the upper wafer W1 will be referred to as the "joining surface W2j," and the surface opposite to the joining surface W2j will be referred to as the "non-joining surface W2n."

[0016] As shown in Figure 1, the joining system 1 comprises an input / output station 2 and a processing station 3. The input / output station 2 and the processing station 3 are arranged in the order of input / output station 2 and processing station 3 along the positive X-axis. The input / output station 2 and the processing station 3 are connected integrally.

[0017] The loading / unloading station 2 comprises a mounting table 10 and a transport area 20. The mounting table 10 comprises a plurality of mounting plates 11. Each mounting plate 11 is fitted with cassettes C1, C2, and C3, which accommodate multiple substrates (for example, 25) in a horizontal position. For example, cassette C1 is a cassette for accommodating the upper wafer W1, cassette C2 is a cassette for accommodating the lower wafer W2, and cassette C3 is a cassette for accommodating the polymerized wafer T.

[0018] The transport area 20 is positioned adjacent to the positive X-axis side of the mounting table 10. This transport area 20 is provided with a transport path 21 extending in the Y-axis direction and a transport device 22 that is movable along this transport path 21.

[0019] The transport device 22 is movable not only in the Y-axis direction but also in the X-axis direction and can rotate around the Z-axis. The transport device 22 transports the upper wafer W1, the lower wafer W2, and the superimposed wafer T between the cassettes C1 to C3 placed on the mounting plate 11 and the third processing block G3 of the processing station 3, which will be described later.

[0020] The number of cassettes C1 to C3 placed on the mounting plate 11 is not limited to those shown in the figure. In addition, cassettes for recovering faulty circuit boards, etc., may be placed on the mounting plate 11 in addition to cassettes C1, C2, and C3.

[0021] The processing station 3 is equipped with multiple processing blocks, for example, three processing blocks G1, G2, and G3, each containing various devices. For example, the first processing block G1 is located on the front side of the processing station 3 (the negative Y-axis side in Figure 1), and the second processing block G2 is located on the rear side of the processing station 3 (the positive Y-axis side in Figure 1). In addition, the third processing block G3 is located on the loading / unloading station 2 side of the processing station 3 (the negative X-axis side in Figure 1).

[0022] The first processing block G1 is equipped with a surface modification apparatus 30 that modifies the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2 with plasma from a processing gas. The surface modification apparatus 30 modifies the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2 by forming unbonded bonds (dangling bonds) through plasma irradiation, thereby making them more easily hydrophilized afterward.

[0023] In the surface modification apparatus 30, for example, a given processing gas is excited and plasma-generated under a reduced-pressure atmosphere and then ionized. The ions of the elements contained in this processing gas are then irradiated onto the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2, thereby plasma-treated and modified the bonding surfaces W1j and W2j. Details of the surface modification apparatus 30 will be described later.

[0024] The second processing block G2 is equipped with a surface hydrophilization device 40 and a bonding device 41. The surface hydrophilization device 40 hydrophilizes the bonding surfaces W1j and W2j of the upper wafer W1 and lower wafer W2 using, for example, pure water, and also cleans the bonding surfaces W1j and W2j.

[0025] In the surface hydrophilization apparatus 40, for example, the upper wafer W1 or lower wafer W2 held in a spin chuck is rotated while pure water is supplied onto the upper wafer W1 or lower wafer W2. As a result, the pure water supplied onto the upper wafer W1 or lower wafer W2 diffuses over the bonding surfaces W1j and W2j of the upper wafer W1 or lower wafer W2, and the bonding surfaces W1j and W2j are made hydrophilic.

[0026] The bonding apparatus 41 bonds the upper wafer W1 and the lower wafer W2. Details of the bonding apparatus 41 will be described later.

[0027] As shown in Figure 2, the third processing block G3 is provided with two stages of transition (TRS) devices 50 and 51 for the upper wafer W1, the lower wafer W2, and the polymerized wafer T, starting from the bottom.

[0028] Furthermore, as shown in Figure 1, a transport area 60 is formed in the region enclosed by the first processing block G1, the second processing block G2, and the third processing block G3. A transport device 61 is arranged in the transport area 60. The transport device 61 has, for example, a transport arm that is movable in the vertical direction, the horizontal direction, and around the vertical axis.

[0029] The transport device 61 moves within the transport area 60 and transports the upper wafer W1, lower wafer W2, and polymerized wafer T to a given device in the first processing block G1, second processing block G2, and third processing block G3 adjacent to the transport area 60.

[0030] The bonding system 1 also includes a control device 4. The control device 4 controls the operation of the bonding system 1. This control device 4 is, for example, a computer and includes a control unit 5 and a storage unit 6. The control unit 5 includes a microcomputer having a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), input / output ports, and various circuits. The CPU of this microcomputer controls the operation of the bonding system 1 by reading and executing a program stored in the ROM. The storage unit 6 is implemented by, for example, a semiconductor memory element such as RAM or flash memory, or a storage device such as a hard disk or optical disc.

[0031] Furthermore, such a program may have been recorded on a computer-readable recording medium and installed from that recording medium into the storage unit 6 of the control device 4. Examples of computer-readable recording media include hard disks (HDs), flexible disks (FDs), compact discs (CDs), magnetic optical discs (MOs), and memory cards.

[0032] <Configuration of the Surface Modification Apparatus> Next, the configuration of the surface modification apparatus 30 will be described with reference to Figure 4. Figure 4 is a schematic cross-sectional view showing the configuration of the surface modification apparatus 30 according to the embodiment.

[0033] As shown in Figure 4, the surface modification apparatus 30 has a processing container 70 that can be sealed inside and accommodate an upper wafer W1 or a lower wafer W2. An inlet / outlet 71 for the upper wafer W1 or lower wafer W2 is formed on the side of the processing container 70 on the transport area 60 side (see Figure 1), and a gate valve 72 is provided at the inlet / outlet 71.

[0034] A stage 80 is positioned inside the processing container 70. The stage 80 is, for example, a lower electrode and is made of a conductive material such as aluminum. A pin through-hole (not shown) is formed in the stage 80, and a lifter pin (not shown) is housed in this pin through-hole. The lifter pin is configured to move up and down by a lifting mechanism (not shown). The stage 80 faces the upper electrode 110, which will be described later, and the space between the stage 80 and the upper electrode 110 forms a plasma generation space 70s for generating plasma from the processing gas.

[0035] The upper surface of the stage 80, that is, the surface facing the upper electrode 110, is a horizontal plane that is circular in plan view and has a larger diameter than the upper wafer W1 and the lower wafer W2. A stage cover 90 is placed on the upper surface of the stage 80, and the upper wafer W1 or the lower wafer W2 is placed on the mounting portion 91 of the stage cover 90.

[0036] A ring-shaped partition plate 103, which has multiple baffle holes, is placed between the stage 80 and the inner wall of the processing container 70. The partition plate 103 is also called an exhaust ring. The partition plate 103 divides the internal space of the processing container 70 into upper and lower sections with the mounting section 91 as the boundary. In addition, the partition plate 103 ensures that the atmosphere inside the processing container 70 is uniformly exhausted from inside the processing container 70.

[0037] A power supply rod 104 made of a conductor is connected to the underside of the stage 80. A high-frequency power supply 106 is connected to the power supply rod 104 via a matching circuit 105, which is made of, for example, a blocking capacitor. During plasma processing, a given high-frequency voltage is applied to the stage 80 from the high-frequency power supply 106.

[0038] Inside the processing container 70, the upper electrode 110 is disposed. The upper surface of the stage 80 and the lower surface of the upper electrode 110 are disposed to face each other in parallel with a given gap therebetween.

[0039] The upper electrode 110 is grounded and connected to the ground potential. Since the upper electrode 110 is thus grounded, damage to the lower surface of the upper electrode 110 can be suppressed during plasma processing.

[0040] As described above, by applying a high-frequency voltage from the high-frequency power source 106 to the stage 80 which is the lower electrode, plasma is generated inside the processing container 70.

[0041] In the embodiment, the stage 80, the power feeding rod 104, the matching unit 105, the high-frequency power source 106, and the upper electrode 110 are an example of a plasma generation unit that generates plasma of a processing gas inside the processing container 70. Note that the high-frequency power source 106 is controlled by the control unit 5 of the control device 4 described above.

[0042] A hollow portion 120 is formed inside the upper electrode 110. A gas supply pipe 121 is connected to the hollow portion 120. A processing gas supply mechanism 122 and a humidified gas supply mechanism 123 are connected to the gas supply pipe 121.

[0043] The processing gas supply mechanism 122 supplies a processing gas to the hollow portion 120 of the upper electrode 110 via the gas supply pipe 121. As the processing gas, for example, oxygen gas, nitrogen gas, argon gas, or the like is used. The processing gas supply mechanism 122 includes a processing gas supply source 122a, a flow rate regulator 122b, and a valve 122c. Then, the processing gas supplied from the processing gas supply source 122a is flow-controlled by the flow rate regulator 122b and the valve 122c, and is supplied to the hollow portion 120 of the upper electrode 110 via the gas supply pipe 121. The processing gas supply mechanism 122 is an example of a first gas supply unit.

[0044] The humidified gas supply mechanism 123 supplies humidified gas (hereinafter referred to as "humidified gas") to the hollow portion 120 of the upper electrode 110 through the gas supply pipe 121. As the humidified gas, for example, humidified nitrogen gas, humidified argon gas, etc. are used. Note that air with adjusted temperature and humidity, etc. may be used as the humidified gas. The humidified gas supply mechanism 123 includes a humidified gas supply source 123a, a flow regulator 123b, and a valve 123c. Then, the humidified gas supplied from the humidified gas supply source 123a is flow-controlled by the flow regulator 123b and the valve 123c, and is supplied to the hollow portion 120 of the upper electrode 110 through the gas supply pipe 121. The humidified gas supply mechanism 123 is an example of the second gas supply unit.

[0045] Inside the hollow portion 120, a baffle plate 126 for promoting uniform diffusion of the processing gas and the humidified gas is provided. A large number of small holes are provided in the baffle plate 126. On the lower surface of the upper electrode 110, a large number of gas ejection openings 125 for ejecting the processing gas and the humidified gas from the hollow portion 120 into the inside of the processing container 70 are formed.

[0046] An exhaust port 130 is formed in the processing container 70. An exhaust pipe 132 that communicates with a vacuum pump 131 for reducing the atmosphere inside the processing container 70 to a given vacuum degree is connected to the exhaust port 130. The exhaust pipe 132 exhausts the inside of the processing container 70 through the exhaust port 130. An APC (Auto Pressure Controller) valve 133 is provided in the exhaust pipe 132. The inside of the processing container 70 is exhausted by the vacuum pump 131 and the exhaust pipe 132, and the pressure inside the processing container 70 is maintained at a predetermined pressure by adjusting the opening degree of the APC valve 133.

[0047] The exhaust pipe 132 is equipped with a laser-type moisture meter 141 capable of measuring the amount of optical attenuation of light of wavelengths that are attenuated by moisture. The laser-type moisture meter 141 irradiates the exhaust passing through the exhaust pipe 132 with laser light and measures the amount of optical attenuation of light of wavelengths that are attenuated by moisture as a value indicating the amount of moisture in the processing container 70. The laser-type moisture meter 141 outputs the measured optical attenuation amount to the control unit 5 of the control device 4. By providing the laser-type moisture meter 141 in the exhaust pipe 132, damage to the laser-type moisture meter 141 due to plasma can be suppressed. The laser-type moisture meter 141 is an example of a first measurement unit.

[0048] In addition, a mass spectrometer (not shown) may be provided in the exhaust pipe 132 instead of the laser moisture meter 141. The mass spectrometer is, for example, a quadrupole mass spectrometer (QMS), which measures the amount of moisture in the processing container 70 by analyzing the atmosphere inside the processing container 70 in terms of the mass number of a specific substance.

[0049] The processing vessel 70 is equipped with a spectrophotometer 142 capable of measuring emission data at various wavelengths within the processing vessel 70. Specifically, the spectrophotometer 142 is mounted on the processing vessel 70 above the mounting section 91 and below the gas nozzle 125. The spectrophotometer 142 is, for example, an OES (Optical Emission Spectroscopy) sensor and measures the emission state of the plasma generated within the processing vessel 70. The spectrophotometer 142 may also be a self-biased OES sensor capable of generating plasma within its own chamber and measuring the emission state of the plasma. The spectrophotometer 142 outputs the measured emission data to the control unit 5 of the control device 4.

[0050] Figure 5 is a magnified view of the vicinity of the inner wall surface 70a of the processing container 70 according to the embodiment. As shown in Figure 5, a porous membrane 73 is formed on the inner wall surface 70a of the processing container 70. The porous membrane 73 has a plurality of pores capable of adsorbing moisture. As a material constituting the porous membrane 73, for example, yttrium oxide (Y) ２ O ３ ) or aluminum oxide (Al ２O ３ Ceramic materials such as ) can be used. By forming a porous membrane 73 on the inner wall surface 70a of the processing container 70, when a humidifying gas is supplied into the processing container 70, moisture contained in the humidifying gas can be efficiently adsorbed onto the porous membrane 73.

[0051] <Configuration of the Joining Device> Next, the configuration of the joining device 41 will be described with reference to Figures 6 and 7. Figure 6 is a schematic plan view showing the configuration of the joining device 41 according to the embodiment, and Figure 7 is a schematic side view showing the configuration of the joining device 41 according to the embodiment.

[0052] As shown in Figure 6, the bonding apparatus 41 has a processing container 190 that can be sealed inside. On the side of the processing container 190 facing the transport area 60, an inlet / outlet 191 for the upper wafer W1, the lower wafer W2, and the polymerized wafer T is formed, and an opening / closing shutter 192 is provided at the inlet / outlet 191.

[0053] The interior of the processing container 190 is divided into a transport area T1 and a processing area T2 by an inner wall 193. The aforementioned loading / unloading port 191 is formed on the side of the processing container 190 in the transport area T1. Furthermore, loading / unloading ports 194 for the upper wafer W1, lower wafer W2, and polymerized wafer T are also formed in the inner wall 193.

[0054] In the transport area T1, the transition 200, the substrate transport mechanism 201, the reversing mechanism 220, and the position adjustment mechanism 210 are arranged in this order, for example, from the input / output 191 side.

[0055] The transition 200 temporarily holds the upper wafer W1, the lower wafer W2, and the polymerized wafer T. The transition 200 is formed in, for example, two stages, and can simultaneously hold any two of the upper wafer W1, the lower wafer W2, and the polymerized wafer T.

[0056] The substrate transport mechanism 201 has transport arms that are movable, for example, in the vertical direction (Z-axis direction), horizontal direction (Y-axis direction, X-axis direction), and direction around the vertical axis (θ direction). The substrate transport mechanism 201 is capable of transporting the upper wafer W1, lower wafer W2, and polymerized wafer T within the transport area T1 or between the transport area T1 and the processing area T2.

[0057] The position adjustment mechanism 210 adjusts the horizontal orientation of the upper wafer W1 and the lower wafer W2. Specifically, the position adjustment mechanism 210 includes a base 211 with a holding part (not shown) that holds and rotates the upper wafer W1 and the lower wafer W2, and a detection unit 212 that detects the position of the notch portion of the upper wafer W1 and the lower wafer W2. The position adjustment mechanism 210 adjusts the position of the notch portion by detecting the position of the notch portion of the upper wafer W1 and the lower wafer W2 using the detection unit 212 while rotating the upper wafer W1 and the lower wafer W2 held on the base 211. This adjusts the horizontal orientation of the upper wafer W1 and the lower wafer W2.

[0058] The inversion mechanism 220 inverts the upper wafer W1 to its front and back sides. Specifically, the inversion mechanism 220 has a holding arm 221 that holds the upper wafer W1. The holding arm 221 extends horizontally (in the X-axis direction). The holding arm 221 is also provided with, for example, four holding members 222 that hold the upper wafer W1.

[0059] The holding arm 221 is supported by a drive unit 223, which is equipped with, for example, a motor. The holding arm 221 is rotatable around a horizontal axis by this drive unit 223. In addition, the holding arm 221 is rotatable around the drive unit 223 and is also movable in the horizontal direction (X-axis direction). Below the drive unit 223, another drive unit (not shown) is provided, which is equipped with, for example, a motor. This other drive unit allows the drive unit 223 to move vertically along the support column 224 that extends vertically.

[0060] Thus, the upper wafer W1 held by the holding member 222 can be rotated around the horizontal axis by the drive unit 223 and can also be moved in the vertical and horizontal directions. Furthermore, the upper wafer W1 held by the holding member 222 can rotate around the drive unit 223 and move between the position adjustment mechanism 210 and the upper chuck 230, which will be described later.

[0061] The processing area T2 is provided with an upper chuck 230 that holds the upper surface (non-bonding surface W1n) of the upper wafer W1 from above by suction, and a lower chuck 231 that holds the lower surface (non-bonding surface W2n) of the lower wafer W2 from below by suction. The lower chuck 231 is provided below the upper chuck 230 and is configured to be positioned opposite the upper chuck 230. The upper chuck 230 and the lower chuck 231 are, for example, vacuum chucks.

[0062] As shown in Figure 7, the upper chuck 230 is supported by a support member 270 provided above the upper chuck 230. The support member 270 is fixed to the ceiling surface of the processing container 190, for example, via a plurality of support columns 271.

[0063] An upper imaging unit 235 is provided on the side of the upper chuck 230 to image the upper surface (bonding surface W2j) of the lower wafer W2 held by the lower chuck 231. For example, a CCD camera is used in the upper imaging unit 235.

[0064] The lower chuck 231 is supported by a first movable part 250 located below it. The first movable part 250 moves the lower chuck 231 horizontally (in the X-axis direction), as will be described later. The first movable part 250 is also configured to allow the lower chuck 231 to move vertically and rotate around a vertical axis.

[0065] The first moving unit 250 is provided with a lower imaging unit 236 that images the lower surface (bonding surface W1j) of the first substrate W1 held by the upper chuck 230. For example, a CCD camera is used for the lower imaging unit 236.

[0066] The first movable part 250 is attached to a pair of rails 252, 252. The pair of rails 252, 252 are provided on the lower side of the first movable part 250 and extend horizontally (in the X-axis direction). The first movable part 250 is configured to be movable along the rails 252.

[0067] A pair of rails 252, 252 are arranged on the second movable section 253. The second movable section 253 is attached to a pair of rails 254, 254. The pair of rails 254, 254 are provided on the lower side of the second movable section 253 and extend horizontally (in the Y-axis direction). The second movable section 253 is configured to be movable horizontally (in the Y-axis direction) along the rails 254. The pair of rails 254, 254 are arranged on a mounting base 255 provided on the bottom surface of the processing container 190.

[0068] The alignment unit 256 is formed by the first moving unit 250 and the second moving unit 253, etc. The alignment unit 256 performs horizontal alignment between the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231 by moving the lower chuck 231 in the X-axis direction, Y-axis direction, and θ direction. The alignment unit 256 also performs vertical alignment between the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231 by moving the lower chuck 231 in the Z-axis direction.

[0069] In this example, the lower chuck 231 is moved in the X-axis, Y-axis, and θ-axis directions. However, the alignment unit 256 may, for example, move the lower chuck 231 in the X-axis and Y-axis directions and the upper chuck 230 in the θ-axis direction. Also, in this example, the lower chuck 231 is moved in the Z-axis direction. However, the alignment unit 256 may, for example, move the upper chuck 230 in the Z-axis direction.

[0070] Next, the configuration of the upper chuck 230 and the lower chuck 231 will be described with reference to Figure 8. Figure 8 is a schematic diagram showing the upper chuck 230 and the lower chuck 231 according to the embodiment.

[0071] As shown in Figure 8, the upper chuck 230 has a main body portion 260. The main body portion 260 is supported by a support member 270. Through holes 266 are formed in the support member 270 and the main body portion 260, penetrating vertically through the support member 270 and the main body portion 260. The position of the through holes 266 corresponds to the center of the upper wafer W1 that is held by the upper chuck 230. The pressing pin 281 of the striker 280 is inserted through the through holes 266.

[0072] The striker 280 is positioned on the upper surface of the support member 270 and comprises a pressing pin 281, an actuator 282, and a linear motion mechanism 283. The pressing pin 281 is a cylindrical member extending along the vertical direction and is supported by the actuator 282.

[0073] The actuator unit 282 generates a constant pressure in a specific direction (here, vertically downward) using air supplied from, for example, an electro-pneumatic regulator (not shown). The actuator unit 282 can contact the center of the upper wafer W1 with the air supplied from the electro-pneumatic regulator and control the pressing load applied to the center of the upper wafer W1. Furthermore, the tip of the actuator unit 282 is able to move up and down vertically by passing through the through hole 266 using air from the electro-pneumatic regulator.

[0074] The actuator unit 282 is supported by the linear motion mechanism 283. The linear motion mechanism 283 moves the actuator unit 282 along the vertical direction by a drive unit, for example, which has a built-in motor.

[0075] The striker 280 is configured as described above, with the linear motion mechanism 283 controlling the movement of the actuator 282, and the actuator 282 controlling the pressing load on the upper wafer W1 by the pressing pin 281. As a result, the striker 280 presses the center of the upper wafer W1, which is held by the upper chuck 230, and brings it into contact with the lower wafer W2.

[0076] The lower surface of the main body 260 is provided with a plurality of pins 261 that contact the upper surface (non-bonding surface W1n) of the upper wafer W1. The plurality of pins 261 have, for example, a diameter of 0.1 mm to 1 mm and a height of several tens of micrometers to several hundred micrometers. The plurality of pins 261 are evenly arranged at intervals of, for example, 2 mm.

[0077] The upper chuck 230 is provided with multiple suction parts for adsorbing the upper wafer W1 in a portion of the area where the multiple pins 261 are provided. Specifically, the lower surface of the main body 260 of the upper chuck 230 is provided with multiple outer suction parts 391 and multiple inner suction parts 392 for adsorbing the upper wafer W1 by vacuuming it. The multiple outer suction parts 391 and the multiple inner suction parts 392 have an arc-shaped suction region in a plan view. The multiple outer suction parts 391 and the multiple inner suction parts 392 are at the same height as the pins 261.

[0078] Multiple external suction parts 391 are arranged on the outer periphery of the main body 260. The multiple external suction parts 391 are connected to a suction device (not shown), such as a vacuum pump, and attract the outer periphery of the upper wafer W1 by vacuum.

[0079] The multiple inner suction portions 392 are arranged radially inward of the main body portion 260, and aligned along the circumferential direction, compared to the multiple outer suction portions 391. The multiple inner suction portions 392 are connected to a suction device (not shown), such as a vacuum pump, and attract the region between the outer periphery and the center of the upper wafer W1 by vacuum.

[0080] The lower chuck 231 has a main body portion 290 having a diameter equal to or larger than that of the lower wafer W2. Here, the lower chuck 231 having a diameter larger than that of the lower wafer W2 is shown. The upper surface of the main body portion 290 is the opposing surface that faces the lower surface (non-bonding surface W2n) of the lower wafer W2.

[0081] The upper surface of the main body 290 is provided with a plurality of pins 291 that contact the lower surface (non-bonding surface Wn2) of the lower wafer W2. The plurality of pins 291 have, for example, a diameter of 0.1 mm to 1 mm and a height of several tens of micrometers to several hundred micrometers. The plurality of pins 291 are evenly arranged at intervals of, for example, 2 mm.

[0082] Furthermore, a lower rib 292 is provided on the upper surface of the main body 290 in an annular shape outside of the multiple pins 291. The lower rib 292 is formed in an annular shape and supports the outer circumference of the lower wafer W2 around its entire circumference.

[0083] Furthermore, the main body 290 has a plurality of lower suction ports 293. The plurality of lower suction ports 293 are provided in the suction area surrounded by the lower ribs 292. The plurality of lower suction ports 293 are connected to a suction device, such as a vacuum pump (not shown), via a suction pipe (not shown).

[0084] The lower chuck 231 reduces the pressure of the adsorption area, which is surrounded by the lower ribs 292, by drawing a vacuum from multiple lower suction ports 293. As a result, the lower wafer W2 placed on the adsorption area is held in place by the lower chuck 231.

[0085] Since the lower rib 292 supports the entire outer circumference of the lower surface of the lower wafer W2, the lower wafer W2 is properly vacuumed up to the outer circumference. This allows the entire surface of the lower wafer W2 to be held by suction. In addition, since the lower surface of the lower wafer W2 is supported by multiple pins 291, when the vacuum of the lower wafer W2 is released, the lower wafer W2 is easily detached from the lower chuck 231.

[0086] <Specific Operation of the Joining System> Next, the specific operation of the joining system 1 according to the embodiment will be described with reference to Figure 9. Figure 9 is a flowchart showing the procedure of processing performed by the joining system 1 according to the embodiment. The various processes shown in Figure 9 are executed based on the control by the control unit 5 of the control device 4.

[0087] First, cassette C1 containing multiple upper wafers W1, cassette C2 containing multiple lower wafers W2, and an empty cassette C3 are placed on a designated mounting plate 11 of the loading / unloading station 2. Then, the upper wafers W1 are removed from cassette C1 by the transport device 22 and transported to the transition device 50 located in the third processing block G3.

[0088] Next, the upper wafer W1 is transported by the transport device 61 to the surface modification apparatus 30 of the first processing block G1. In the surface modification apparatus 30, nitrogen gas, which is the processing gas, is excited and plasma-generated and ionized under a predetermined reduced-pressure atmosphere. These nitrogen ions are irradiated onto the bonding surface W1j of the upper wafer W1, and the bonding surface W1j is plasma-treated. As a result, the bonding surface W1j of the upper wafer W1 is modified (step S101). Here, the surface modification apparatus 30 adjusts the moisture content in the processing container 70 by supplying a small flow rate of humidifying gas into the processing container 70 prior to vacuuming the processing container 70, and by supplying a large flow rate of humidifying gas into the processing container 70 after vacuuming and before plasma generation. Then, with the moisture content in the processing container 70 adjusted by a large flow rate of humidifying gas, the surface modification apparatus 30 modifies the bonding surface W1j of the upper wafer W1 by generating plasma of the processing gas in the processing container 70.

[0089] As described above, the surface modification apparatus 30 according to this embodiment modifies the bonding surface W1j of the upper wafer W1 after vacuuming and before plasma generation, while the moisture content in the processing container 70 is adjusted by a large flow rate of humidifying gas. This makes it possible to suppress the decrease in bonding strength between the upper wafer W1 and the lower wafer W2 that occurs when the upper wafer W1 and the lower wafer W2 are bonded together. The factors that suppress the decrease in bonding strength between the upper wafer W1 and the lower wafer W2 will be described later.

[0090] Next, the upper wafer W1 is transported by the transport device 61 to the surface hydrophilization device 40 of the first processing block G1. In the surface hydrophilization device 40, pure water is supplied onto the upper wafer W1 while it is rotated, which is held in a spin chuck. This makes the bonding surface W1j of the upper wafer W1 hydrophilic. In addition, the bonding surface W1j of the upper wafer W1 is cleaned by the pure water (step S102).

[0091] Next, the upper wafer W1 is transported by the transport device 61 to the bonding device 41 of the second processing block G2. The upper wafer W1, once loaded into the bonding device 41, is transported via the transition 200 to the position adjustment mechanism 210, where its horizontal orientation is adjusted (step S103).

[0092] Subsequently, the upper wafer W1 is transferred from the position adjustment mechanism 210 to the inversion mechanism 220, and the inversion mechanism 220 inverts the front and back surfaces of the upper wafer W1 (step S104). Specifically, the bonding surface W1j of the upper wafer W1 is oriented downwards.

[0093] Next, the upper wafer W1 is transferred from the reversal mechanism 220 to the upper chuck 230, and the upper wafer W1 is held in place by the upper chuck 230 (step S105).

[0094] The processing of the lower wafer W2 is performed in overlap with the processing of the upper wafer W1 in steps S101 to S105. First, the lower wafer W2 is removed from the cassette C2 by the transport device 22 and transported to the transition device 50 located in the third processing block G3.

[0095] Next, the lower wafer W2 is transported to the surface modification apparatus 30 by the transport device 61, and the bonding surface W2j of the lower wafer W2 is modified (step S106). Step S106 is the same process as step S101 described above, and is performed with the moisture content in the processing container 70 adjusted.

[0096] Subsequently, the lower wafer W2 is transported by the transport device 61 to the surface hydrophilization device 40, where the bonding surface W2j of the lower wafer W2 is hydrophilized and the bonding surface W2j is cleaned (step S107).

[0097] Subsequently, the lower wafer W2 is transported to the bonding apparatus 41 by the transport device 61. The lower wafer W2, once loaded into the bonding apparatus 41, is transported to the position adjustment mechanism 210 via the transition 200. The position adjustment mechanism 210 then adjusts the horizontal orientation of the lower wafer W2 (step S108).

[0098] Subsequently, the lower wafer W2 is transported to the lower chuck 231 and held by suction with the notch portion facing a predetermined direction (step S109).

[0099] Next, the horizontal position adjustment is performed between the upper wafer W1 held in the upper chuck 230 and the lower wafer W2 held in the lower chuck 231 (step S110).

[0100] Next, the vertical position of the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231 is adjusted (step S111). Specifically, the first moving unit 250 moves the lower chuck 231 vertically upward, bringing the lower wafer W2 closer to the upper wafer W1.

[0101] Next, after releasing the suction hold of the upper wafer W1 by the multiple internal suction parts 392 (step S112), the center of the upper wafer W1 is pressed down by lowering the pressing pin 281 of the striker 280 (step S113).

[0102] When the center of the upper wafer W1 comes into contact with the center of the lower wafer W2, and the centers of the upper wafer W1 and the lower wafer W2 are pressed together by the striker 280 with a predetermined force, bonding begins between the pressed centers of the upper wafer W1 and the lower wafer W2. That is, since the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 are modified, van der Waals forces (intermolecular forces) are first generated between the bonding surfaces W1j and W2j, and the bonding surfaces W1j and W2j are joined together. Furthermore, since the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 are hydrophilic, the hydrophilic groups between the bonding surfaces W1j and W2j form hydrogen bonds, and the bonding surfaces W1j and W2j are firmly joined together. In this way, a bonding region is formed.

[0103] Subsequently, a bonding wave is generated between the upper wafer W1 and the lower wafer W2, in which the bonding region expands from the center to the outer periphery of both the upper wafer W1 and the lower wafer W2. Then, the suction holding of the upper wafer W1 by the multiple outer suction parts 391 is released (step S114). As a result, the outer periphery of the upper wafer W1, which was held by the outer suction parts 391, falls. Consequently, the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 come into full contact, and a polymerized wafer T is formed.

[0104] Subsequently, the pressing pin 281 is raised to the upper chuck 230, releasing the suction holding of the lower wafer W2 by the lower chuck 231. Then, the polymerized wafer T is discharged from the bonding apparatus 41 by the transport device 61. In this way, the series of bonding processes is completed.

[0105] Figure 10 is a timing chart showing the operation of each part when modifying the bonding surfaces W1j and W2j of the upper wafer W1 and lower wafer W2 in the bonding process according to the embodiment. Note that Figure 10 shows the timing chart from the point when the transport of the upper wafer W1 to the surface modification apparatus 30 begins, before the above-described step S101 (modification of the bonding surface W1j of the upper wafer W1) is started.

[0106] As a result of diligent research, the inventors of this application have found that adjusting the amount of moisture in the processing container 70 with a large flow rate of humidifying gas promotes the formation of dangling bonds that contribute to bonding at the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2. Therefore, in the surface modification apparatus 30 according to this embodiment, prior to surface modification of the upper wafer W1 by the plasma of the processing gas, the amount of moisture in the processing container 70 is adjusted by supplying a large flow rate of humidifying gas into the processing container 70.

[0107] Figures 11 and 12 illustrate an example of the measurement results of the moisture content in the processing container 70. Figure 11 shows emission data at various wavelengths inside the processing container 70 immediately after it is opened to the atmosphere during maintenance. Figure 11 shows emission data measured by the spectrophotometer 142 when a nitrogen gas plasma, which is the processing gas, is generated inside the processing container 70. The nitrogen gas plasma contains nitrogen ions in the first excited state (1st POS) and nitrogen ions in the second excited state (2st POS), which are more active than nitrogen ions in the first excited state. The wavelength of nitrogen ions in the first excited state is in the range of approximately 530 nm to 800 nm, and the wavelength of nitrogen ions in the second excited state is in the range of approximately 280 nm to 440 nm. The emission data shown in Figure 11 indicates that when the processing container 70 is opened to the atmosphere during maintenance, almost no nitrogen ions in the first excited state are generated. This is thought to be because the amount of moisture in the processing container 70 increased due to the release of air, and the energy of the nitrogen ions in the first excited state was transferred to the moisture (H2O) present in the processing container 70, causing the nitrogen ions in the first excited state to disappear from the processing container 70.

[0108] Figure 12 shows emission data at various wavelengths inside the processing container 70 after the surface modification of the upper wafer W1 has been repeated a predetermined number of times. Figure 12 shows emission data measured by the spectrophotometer 142 when a plasma of nitrogen gas, which is the processing gas, is generated inside the processing container 70. The emission data shown in Figure 12 indicates that when the surface modification of the upper wafer W1 is repeated inside the processing container 70, the amount of nitrogen ions in the first excited state increases. This is thought to be because, when the surface modification is repeated, the amount of water inside the processing container 70 decreases due to vacuuming, etc., making it more difficult for the energy of nitrogen ions in the first excited state to be transferred to water (H2O), and thus increasing the amount of nitrogen ions remaining in the first excited state.

[0109] In the surface modification apparatus 30 according to this embodiment, prior to surface modification of the upper wafer W1 by plasma of the processing gas, the amount of moisture in the processing container 70 is adjusted by supplying a large flow rate of humidifying gas into the processing container 70. As a result, the amount of moisture in the processing container 70 increases, creating a state in which a large amount of moisture (H2O) exists near the bonding surface W1j of the upper wafer W1.

[0110] In this state, the upper wafer W1 is subjected to a surface modification treatment using a nitrogen gas plasma, which is the processing gas. At this time, among the nitrogen ions in the first excited state and the nitrogen ions in the second excited state contained in the nitrogen gas plasma, the energy of the nitrogen ions in the first excited state, which have relatively lower activity, is transferred to the water (H2O) present near the junction surface W1j.

[0111] As a result, the nitrogen ions in the first excited state decrease within the processing container 70, while the proportion of nitrogen ions in the second excited state, which are more active than those in the first excited state, increases. Consequently, nitriding by nitrogen ions in the first excited state can be suppressed while irradiating the junction surface W1j with nitrogen ions in the second excited state, which are relatively more active, thereby promoting the formation of dangling bonds of silicon atoms on the outermost surface of the junction surface W1j. On the other hand, since nitriding by nitrogen ions in the first excited state is suppressed on the outermost surface of the junction surface W1j, the generation of nitrided portions is reduced.

[0112] Thus, in this embodiment, by adjusting the amount of moisture in the processing container 70 with a large flow rate of humidifying gas after vacuuming and before plasma generation, the formation of dangling bonds can be promoted at the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2. In other words, in this embodiment, by adjusting the amount of moisture in the processing container 70, the formation of dangling bonds that contribute to the bonding of the upper wafer W1 and the lower wafer W2 can be promoted while suppressing the generation of nitrided portions that hinder the bonding of the upper wafer W1 and the lower wafer W2. Therefore, according to this embodiment, it is possible to suppress a decrease in bonding strength between the upper wafer W1 and the lower wafer W2 to be bonded.

[0113] Returning to the explanation of Figure 10, the control unit 5 operates the humidifying gas supply mechanism 123 from time T10, when the transport of the upper wafer W1 to the surface modification apparatus 30 begins, to supply humidifying gas into the processing container 70 at a first flow rate. The first flow rate is, for example, 10 sccm or more and 100 sccm or less. The value of the first flow rate is just an example and is determined appropriately, for example, according to the volume of the processing container 70. The control unit 5 also adjusts the internal pressure of the processing container 70 to the initial value, the first pressure, by adjusting the opening of the APC valve 133 to the first opening.

[0114] At time T11, a predetermined time after time T10, the control unit 5 raises the lifter pin from the stage 80, and at time T12, a predetermined time after time T11, it opens the gate valve 72. At time T13, a predetermined time after time T12, the control unit 5 extends the transport arm of the transport device 61 into the processing container 70 and transfers the upper wafer W1 held on the transport arm to the lifter pin. At time T14, when the transport arm of the transport device 61 has exited the processing container 70, the control unit 5 closes the gate valve 72. Then, at time T15, a predetermined time after time T14, the control unit 5 stops the humidifying gas supply mechanism 123, ending the loading of the upper wafer W1 into the processing container 70. The period from time T10 to time T15 is called the "waiting period".

[0115] Thus, during the standby period, the control unit 5 adjusts the moisture content in the processing container 70 by supplying humidifying gas to the processing container 70 at a first flow rate. The moisture content in the processing container 70 is adjusted to, for example, a range of 3,000 ppm to 10,000 ppm. The process of adjusting the moisture content in the processing container 70 by supplying humidifying gas to the processing container 70 at a first flow rate during the standby period is an example of the first adjustment step.

[0116] During the execution of the first adjustment process, the control unit 5 can measure a value indicating the amount of moisture in the processing container 70 using a laser moisture meter 141. In this case, the control unit 5 may control the flow rate or moisture content of the humidifying gas based on the measured value indicating the amount of moisture in the processing container 70. Specifically, the control unit 5 measures the amount of light attenuation measured by the laser moisture meter 141 as a value indicating the amount of moisture in the processing container 70. Then, the control unit 5 controls the flow rate or moisture content of the humidifying gas based on the measured amount of light attenuation. The measured value of light attenuation by the laser moisture meter 141 decreases as the amount of moisture in the processing container 70 decreases. For example, the control unit 5 determines whether the measured value of light attenuation is within an acceptable range. If the control unit 5 determines that the measured value of light attenuation is below the lower limit of the acceptable range, it controls the humidifying gas supply mechanism 123 to increase the flow rate or moisture content of the humidifying gas. On the other hand, if the control unit 5 determines that the measured value of light attenuation is above the upper limit of the acceptable range, it decreases the flow rate or moisture content of the humidifying gas. This allows the control unit 5 to adjust the amount of moisture in the processing container 70 within an appropriate range (for example, between 3,000 ppm and 10,000 ppm). However, if the measured value of the optical attenuation exceeds the upper limit of the allowable range, that is, if the amount of moisture in the processing container 70 is greater than the appropriate amount, oxidation and hydroxylation of the bonding surface W1j of the upper wafer W1 to be activated will progress, which may reduce the bonding strength between the upper wafer W1 and the lower wafer W2.

[0117] The control unit 5 evacuates the processing container 70 by adjusting the opening of the APC valve 133 from its initial value, the first opening, to fully open, starting at time T15, which is the end of the standby period. As a result, the pressure inside the processing container 70 is adjusted from the initial value, the first pressure, to a pressure lower than the first pressure. The process of evacuating the processing container 70 during the period from time T15 to time T17, which will be described later, is an example of a vacuuming process.

[0118] The control unit 5 places the upper wafer W1 onto the stage 80 by lowering the lifter pin toward the stage 80 at time T16, which is a predetermined time after time T15.

[0119] The control unit 5 adjusts the opening of the APC valve 133 from fully open to a second opening that is less than fully open but greater than the first opening, starting from time T17, which is a predetermined time after time T16. As a result, the pressure inside the processing container 70 is adjusted to a second pressure that is lower than the first pressure. The second pressure is the process pressure used for the surface modification treatment.

[0120] After the pressure inside the processing container 70 reaches the process pressure (i.e., the second pressure), i.e., after the vacuuming process, the control unit 5 operates the humidifying gas supply mechanism 123 from time T18 to supply humidifying gas into the processing container 70 at a second flow rate greater than the first flow rate. The second flow rate is, for example, 300 sccm or more and 500 sccm or less. The value of the second flow rate is an example and is determined appropriately, for example, according to the volume of the processing container 70.

[0121] Thus, after the vacuuming process and before the plasma of the processing gas is generated in the processing container 70, the control unit 5 adjusts the amount of moisture in the processing container 70 by supplying humidifying gas into the processing container 70 at a second flow rate greater than the first flow rate. The amount of moisture in the processing container 70 is adjusted to, for example, a range of 3,000 ppm to 10,000 ppm. The first flow rate is appropriately referred to as the "low flow rate," and the second flow rate is appropriately referred to as the "high flow rate." The process of adjusting the amount of moisture in the processing container 70 by supplying humidifying gas into the processing container 70 at a second flow rate after the vacuuming process and before the plasma of the processing gas is generated in the processing container 70 is an example of the second adjustment process.

[0122] After the vacuuming process, prior to the generation of plasma from the processing gas, the amount of moisture in the processing container 70 can be adjusted with a large flow rate of humidifying gas to compensate for the decrease in moisture in the processing container 70 caused by plasma generation. As a result, even if the amount of moisture in the processing container 70 decreases due to plasma generation, the formation of dangling bonds that contribute to bonding can be promoted at the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2. In other words, in this embodiment, by adjusting the amount of moisture in the processing container 70 using a large flow rate of humidifying gas, the generation of nitrided portions that hinder bonding of the upper wafer W1 and the lower wafer W2 can be suppressed while promoting the formation of dangling bonds that contribute to bonding. Therefore, according to this embodiment, a decrease in bonding strength between the upper wafer W1 and the lower wafer W2 to be bonded can be suppressed.

[0123] Furthermore, during the period from time T18 to time T19, the control unit 5 changes the opening degree of the APC valve 133 from the second opening degree to a third opening degree, which is smaller than the first and second opening degrees. By changing the opening degree of the APC valve 133 to the third opening degree, the pressure inside the processing vessel 70 is adjusted from the process pressure (i.e., the second pressure) to a third pressure that is higher than the first pressure and the process pressure. In other words, the second adjustment step is performed with the pressure inside the processing vessel 70 adjusted to a higher pressure than the pressure inside the processing vessel 70 in the first adjustment step.

[0124] Thus, in the second adjustment step, humidifying gas is supplied into the processing container 70 under higher pressure conditions compared to the first adjustment step. This allows the humidifying gas to be supplied into the processing container 70 while increasing the amount of saturated water vapor in the atmosphere inside the processing container 70. As a result, more moisture contained in the humidifying gas can be retained in the atmosphere inside the processing container 70.

[0125] Furthermore, during the execution of the second adjustment process, the control unit 5 can measure a value indicating the amount of moisture in the processing container 70 using a laser moisture meter 141. In this case, the control unit 5 may control the flow rate or moisture content of the humidifying gas based on the measured value indicating the amount of moisture in the processing container 70. Specifically, the control unit 5 measures the amount of light attenuation measured by the laser moisture meter 141 as a value indicating the amount of moisture in the processing container 70. Then, the control unit 5 controls the flow rate or moisture content of the humidifying gas based on the measured amount of light attenuation. The measured value of light attenuation by the laser moisture meter 141 decreases as the amount of moisture in the processing container 70 decreases. For example, the control unit 5 determines whether the measured value of light attenuation is within an acceptable range. If the control unit 5 determines that the measured value of light attenuation is below the lower limit of the acceptable range, it controls the humidifying gas supply mechanism 123 to increase the flow rate or moisture content of the humidifying gas. On the other hand, if the control unit 5 determines that the measured value of light attenuation is above the upper limit of the acceptable range, it decreases the flow rate or moisture content of the humidifying gas. As a result, the control unit 5 can adjust the amount of moisture in the processing container 70 within an appropriate range (for example, within the range of 3,000 ppm to 10,000 ppm). However, if the measured value of the optical attenuation exceeds the upper limit of the allowable range, that is, if the amount of moisture in the processing container 70 is greater than the appropriate amount, oxidation and hydroxylation of the bonding surface W1j of the upper wafer W1 to be activated will progress, and the bonding strength between the upper wafer W1 and the lower wafer W2 will decrease.

[0126] The control unit 5 stops the humidifying gas supply mechanism 123 at time T19, which is a predetermined time after time T18. This allows the control unit 5 to stop supplying humidifying gas prior to the generation of the processing gas plasma. If humidifying gas is supplied during plasma generation, a water plasma (i.e., plasma containing hydroxyl radicals "•OH") is directly generated by H2O. This water plasma may corrode the exposed metal parts of the circuit, such as Cu, on the bonding surfaces W1j and W2j (i.e., the activation surfaces) of the upper wafer W1 and lower wafer W2. Therefore, supplying humidifying gas during plasma generation is undesirable from a process perspective. For this reason, the control unit 5 stops supplying humidifying gas prior to the generation of the processing gas plasma.

[0127] From time T19, the control unit 5 adjusts the opening of the APC valve 133 from the third opening to a second opening, which is greater than both the first and third openings. As a result, the pressure inside the processing vessel 70 is adjusted from the third pressure to a process pressure (i.e., the second pressure) that is lower than both the first and third pressures.

[0128] Furthermore, from time T19, the control unit 5 operates the processing gas supply mechanism 122 to supply nitrogen gas, which is the processing gas, into the processing container 70. Then, at time T20, a predetermined time after time T19, the control unit 5 controls the high-frequency power supply 106 to apply a high-frequency voltage to the stage 80, thereby generating nitrogen gas plasma in the processing container 70.

[0129] The nitrogen ions in the plasma generated in this way are irradiated onto the bonding surface W1j of the upper wafer W1, thereby modifying the bonding surface W1j. As a result, dangling bonds of silicon atoms are formed on the outermost surface of the bonding surface W1j.

[0130] At time T21, a predetermined time after time T20, the control unit 5 stops the high-frequency power supply 106 and adjusts the opening of the APC valve 133 from the second opening to the first opening, thereby returning the pressure inside the processing container 70 to the initial pressure. Then, at time T22, when the pressure inside the processing container 70 reaches the initial pressure, the control unit 5 raises the lifter pin from the stage 80 to position the modified upper wafer W1 above the stage 80. Then, at time T23, a predetermined time after time T22, the control unit 5 stops the processing gas supply mechanism 122.

[0131] At time T24, a predetermined time after time T23, the control unit 5 operates the humidifying gas supply mechanism 123 to supply humidifying gas into the processing container 70. This causes the control unit 5 to replace the nitrogen gas remaining in the processing container 70 with the humidifying gas. Then, at time T25, a predetermined time after time T24, the control unit 5 completely replaces the nitrogen gas remaining in the processing container 70 with the humidifying gas, thereby completing the modification of the bonding surface W1j of the upper wafer W1. The process of modifying the bonding surface W1j of the upper wafer W1 by generating a plasma of processing gas (in this case, nitrogen gas) in the processing container 70 is an example of a modification process.

[0132] Furthermore, during the execution of the modification process, the control unit 5 may control the spectrophotometer 142 to acquire emission data of nitrogen gas supplied into the processing container 70 and measure the value of the peak generated at the wavelength corresponding to the nitrogen ion of the first excited state in the emission data. As the amount of moisture in the processing container 70 decreases, the value of the peak generated at the wavelength corresponding to the nitrogen ion of the first excited state increases (see Figures 11 and 12). Therefore, from the value of the peak generated at the wavelength corresponding to the nitrogen ion of the first excited state, it is possible to determine whether the bonding strength between the upper wafer W1 and the lower wafer W2 has decreased below the normal range due to the decrease in the amount of moisture in the processing container 70. For example, the control unit 5 determines whether the value of the peak generated at the wavelength corresponding to the nitrogen ion of the first excited state, as measured by the spectrophotometer 142, is above a threshold. The threshold is a value at which the bonding strength between the upper wafer W1 and the lower wafer W2 can be considered to have decreased below the normal range. For example, the threshold is the value of one peak arbitrarily selected from the values ​​of multiple peaks that occur when the bonding strength between the upper wafer W1 and the lower wafer W2 falls within a normal range. The control unit 5 determines that the bonding strength between the upper wafer W1 and the lower wafer W2 is within a normal range and is good if the value of the peak that occurs at the wavelength corresponding to the nitrogen ion of the first excited state, as measured by the spectrophotometer 142, is below the threshold. On the other hand, the control unit 5 determines that the bonding strength between the upper wafer W1 and the lower wafer W2 is below a normal range and is defective if the value of the peak that occurs at the wavelength corresponding to the nitrogen ion of the first excited state, as measured by the spectrophotometer 142, exceeds the threshold, and outputs an alert. This allows the user to be notified that the bonding strength between the upper wafer W1 and the lower wafer W2 is poor before bonding the upper wafer W1 and the lower wafer W2.

[0133] Furthermore, at time T25, the control unit 5 opens the gate valve 72. At time T26, after a predetermined time has elapsed from time T245, the control unit 5 extends the transport arm of the transport device 61 into the processing container 70 and transfers the modified upper wafer W1, which is positioned above the stage 80, to the transport arm. Subsequently, the control unit 5 transports the modified upper wafer W1 to the surface hydrophilization device 40 using the transport device 61.

[0134] When the modified upper wafer W1 is transported to the surface hydrophilization device 40, the transport of the unmodified lower wafer W2 to the surface modification device 30 begins. That is, the control unit 5 holds the lower wafer W2 on the transport arm of the transport device 61 and moves the transport device 61 to the surface modification device 30. At time T27, when the transport device 61 reaches the surface modification device 30, the control unit 5 extends the transport arm of the transport device 61 into the processing container 70 and transfers the lower wafer W2 held on the transport arm to the lifter pin. At time T28, when the transport arm of the transport device 61 exits from the processing container 70, the control unit 5 closes the gate valve 72. After that, the control unit 5 waits from time T28 until time T29, which is a predetermined time elapsed. In this way, during the period from time T25 to time T29, the unmodified lower wafer W2 is transported into the processing container 70 in place of the modified upper wafer W1. Hereafter, the period from time T25 to time T29, which is the end of the process period, will be referred to as the "wafer replacement period." Then, from time T29 onward, which is the end of the wafer replacement period, processing is performed on the lower wafer W2 in the same way as the processing performed on the upper wafer W1 during the process period. As a result, the bonding surface W1j of the lower wafer W2 is modified. Once the modification of the lower wafer W2 is complete, the control unit 5 can remove the modified lower wafer W2 from the surface modification apparatus 30 using the transport device 61.

[0135] Thus, in this embodiment, after vacuuming and before plasma generation, the amount of moisture in the processing container 70 is adjusted with a large flow rate of humidifying gas, and with the moisture content in the processing container 70 adjusted, the bonding surface W1j of the upper wafer W1 is modified by the plasma of the processing gas. This makes it possible to suppress a decrease in bonding strength between the upper wafer W1 and the lower wafer W2 to be bonded.

[0136] In other words, in this embodiment, prior to modifying the upper wafer W1, the amount of moisture in the processing container 70 is adjusted by supplying a humidifying gas into the processing container 70 capable of housing the upper wafer W1. As a result, the amount of moisture in the processing container 70 increases, creating a state in which a large amount of moisture (H2O) exists near the bonding surface W1j of the upper wafer W1.

[0137] In this state, the upper wafer W1 is subjected to a surface modification treatment using a nitrogen gas plasma, which is the processing gas. At this time, among the nitrogen ions in the first excited state and the nitrogen ions in the second excited state contained in the nitrogen gas plasma, the energy of the nitrogen ions in the first excited state, which have relatively lower activity, is transferred to the water (H2O) present near the junction surface W1j.

[0138] As a result, nitrogen ions in the first excited state disappear from within the processing container 70, while the proportion of nitrogen ions in the second excited state, which are more active than those in the first excited state, increases. Consequently, nitriding by nitrogen ions in the first excited state can be suppressed while the relatively more active nitrogen ions in the second excited state can be irradiated onto the junction surface W1j, thereby promoting the formation of dangling bonds of silicon atoms on the outermost surface of the junction surface W1j. On the other hand, since nitriding by nitrogen ions in the first excited state is suppressed on the outermost surface of the junction surface W1j, the generation of nitrided portions is reduced.

[0139] In this state, when the upper wafer W1 is removed from the surface modification apparatus 30 and exposed to the atmosphere, the dangling bonds of silicon atoms are terminated with OH groups due to moisture (H2O) in the atmosphere.

[0140] Here, since the generation of nitrided portions is reduced at the outermost surface of the bonding surface W1j, the formation of OH groups is not inhibited by such nitrided portions.

[0141] Next, the upper wafer W1 and lower wafer W2, which have been removed from the surface modification apparatus 30, undergo hydrophilic treatment of the bonding surfaces W1j and W2j in the surface hydrophilization apparatus 40, and are then bonded in the bonding apparatus 41. In this bonding process, a bond is formed from the center to the edge of the wafer W by hydrogen bonding between the OH groups of the bonding surface W1j and the OH groups of the bonding surface W2j.

[0142] In this embodiment, since the occurrence of nitrided portions on the outermost surface of the bonding surface W1j is reduced, the bonding caused by the OH groups described above is not inhibited by such nitrided portions. In other words, in this embodiment, the occurrence of nitrided portions that inhibit the formation of Si-O-Si bonds starting from OH groups can be suppressed by adjusting the amount of moisture in the processing container 70. Therefore, according to this embodiment, it is possible to suppress the decrease in bonding strength between the upper wafer W1 and the lower wafer W2 to be bonded.

[0143] <Effects> As described above, the surface modification method according to the embodiment is a surface modification method that modifies the bonding surfaces (for example, bonding surfaces W1j and W2j) of a substrate (for example, an upper wafer W1 and a lower wafer W2) that are bonded to another substrate (for example, an upper wafer W1 and a lower wafer W2) by plasma of a processing gas, and includes a first adjustment step, a vacuuming step, a second adjustment step, and a modification step. The first adjustment step adjusts the amount of moisture in the processing container by supplying humidified gas at a first flow rate into a processing container (for example, a processing container 70) capable of housing the substrate. The vacuuming step evacuates the processing container after the first adjustment step. The second adjustment step adjusts the amount of moisture in the processing container by supplying humidified gas at a second flow rate greater than the first flow rate into the processing container. The modification step modifies the bonding surfaces of the substrate by generating plasma of the processing gas in the processing container after the second adjustment step. This makes it possible to suppress a decrease in bonding strength between the substrates to be bonded.

[0144] Furthermore, the second adjustment step may be performed with the pressure inside the processing container adjusted to a higher pressure (for example, a third pressure) than the pressure inside the processing container in the first adjustment step (for example, a second pressure). This allows more moisture contained in the humidifying gas to remain in the atmosphere inside the processing container.

[0145] Furthermore, the processing container may have a porous membrane (for example, a porous membrane 73) on its inner wall surface. This allows the porous membrane to efficiently adsorb moisture contained in the humidifying gas when it is supplied into the processing container.

[0146] Furthermore, the surface modification method according to the embodiment may further include a first measurement step of measuring a value indicating the amount of moisture in the treatment container during the execution of the first or second adjustment step. The first or second adjustment step may control the flow rate or moisture content of the humidified gas based on the value indicating the amount of moisture in the treatment container measured in the first measurement step. This makes it possible to adjust the amount of moisture in the treatment container within an appropriate range.

[0147] Furthermore, the first measurement step may be performed using a first measurement unit (for example, a laser-type moisture meter 141) that measures a value indicating the amount of moisture in the processing container. The first measurement unit may be provided in the exhaust pipe that exhausts the inside of the processing container. This makes it possible to suppress damage to the first measurement unit by plasma.

[0148] Furthermore, the surface modification method according to the embodiment may further include a second measurement step in which emission data of the processing gas is acquired during the execution of the modification step, and the value of a peak occurring at a specific wavelength in the emission data is measured. The modification step may output an alert if the value of the peak measured in the second measurement step exceeds a threshold. This allows the user to be notified that the bonding strength between the substrates is poor before the substrates are bonded together.

[0149] Furthermore, the processing container may be provided with a mounting section for placing the substrate (for example, a mounting section 91) and a gas outlet (for example, a gas outlet 125) positioned above the mounting section for ejecting processing gas into the processing container. The second measurement step may be performed using a second measurement unit (for example, a spectrophotometer 142) for measuring peak values. The second measurement unit may be positioned above the mounting section and below the gas outlet. This makes it possible to appropriately measure the peak values ​​that occur at specific wavelengths in the emission data.

[0150] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The above embodiments may be omitted, replaced, or modified in various forms without departing from the scope and spirit of the appended claims.

[0151] 1 Bonding system 5 Control unit 30 Surface modification device 41 Bonding device 70 Processing container 80 Stage 91 Mounting unit 104 Power supply rod 105 Matching unit 106 High-frequency power supply 110 Upper electrode 122 Processing gas supply mechanism 123 Humidifying gas supply mechanism 125 Gas nozzle 141 Laser moisture meter 142 Spectrophotometer W1 Upper wafer W2 Lower wafer

Claims

1. A surface modification method for modifying a bonding surface of a substrate that is bonded to another substrate by plasma of a processing gas, comprising: a first adjustment step of adjusting the amount of moisture in a processing container by supplying humidified gas at a first flow rate into a processing container capable of containing the substrate; a vacuuming step of evacuating the processing container after the first adjustment step; a second adjustment step of adjusting the amount of moisture in the processing container by supplying humidified gas at a second flow rate greater than the first flow rate into the processing container after the vacuuming step and before plasma of the processing gas is generated in the processing container; and a modification step of modifying the bonding surface of the substrate by generating plasma of the processing gas in the processing container after the second adjustment step.

2. The surface modification method according to claim 1, wherein the second adjustment step is performed while the pressure inside the processing container is adjusted to a higher pressure than the pressure inside the processing container in the first adjustment step.

3. The surface modification method according to claim 1, wherein the processing container has a porous membrane on its inner wall surface.

4. The surface modification method according to claim 1, further comprising a first measurement step of measuring a value indicating the amount of moisture in the processing container during the execution of the first adjustment step or the second adjustment step, wherein the first adjustment step or the second adjustment step controls the flow rate or moisture content of the humidified gas based on the value indicating the amount of moisture in the processing container measured in the first measurement step.

5. The surface modification method according to claim 4, wherein the first measurement step is performed using a first measuring unit that measures a value indicating the amount of moisture in the processing container, and the first measuring unit is provided in an exhaust pipe that exhausts the inside of the processing container.

6. The surface modification method according to claim 1, further comprising a second measurement step of acquiring emission data of the processed gas during the execution of the modification step and measuring the value of a peak occurring at a specific wavelength in the emission data, wherein the modification step outputs an alert when the value of the peak measured in the second measurement step exceeds a threshold.

7. The surface modification method according to claim 6, wherein the processing container is provided with a mounting section for placing the substrate and a gas nozzle positioned above the mounting section for ejecting the processing gas into the processing container, the second measurement step is performed using a second measurement unit for measuring the peak value, and the second measurement unit is positioned above the mounting section and below the gas nozzle.

8. A surface modification apparatus for modifying a bonding surface of a substrate that is bonded to another substrate by plasma of a processing gas, comprising: a processing container capable of containing the substrate; a first gas supply unit for supplying the processing gas into the processing container; a second gas supply unit for supplying humidified gas into the processing container; a vacuum unit for evacuating the processing container; a plasma generation unit and a control unit for generating plasma of the processing gas into the processing container, wherein the control unit performs: a first adjustment step of adjusting the amount of moisture in the processing container by supplying humidified gas into the processing container at a first flow rate; a vacuum evacuation step of evacuating the processing container after the first adjustment step; a second adjustment step of adjusting the amount of moisture in the processing container by supplying humidified gas into the processing container at a second flow rate greater than the first flow rate before plasma of the processing gas is generated in the processing container after the vacuum evacuation step; and a modification step of modifying the bonding surface of the substrate by generating plasma of the processing gas in the processing container after the second adjustment step.

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